1. Field of the Invention
The present invention relates generally to the field of centrifugal fans or blowers, and more particularly to an improved blower wheel or impeller of the type especially useful for portable room air cleaners or humidifiers.
2. Description of the Related Art
Blower wheels or impellers and methods of manufacturing the same are well known in the art and a wide variety of blowers are commercially available. Typically, portable room air cleaners and humidifiers utilize centrifugal fans to draw ambient air through the device during operation.
Single and dual input blower wheels or impellers for centrifugal fans of this type generally include an annular, rotary base plate or hub on which is mounted a plurality of peripherally-spaced, axial fan blades or vanes. A single input blower wheel has a single axial input formed by a single set of blades projecting from one side of the base plate. In contrast, a dual input blower wheel comprises two sets of blades projecting from opposite sides of the base plate, thereby forming two axial inputs. Each set of blades of the conventional dual input blower wheel is of the same length so that the distal ends of the blades are equidistant from the base plate.
Whether a single or a dual input blower wheel, the operation is generally as follows. The hub of the blower wheel is secured to the drive shaft of a driving motor, whereby the blower wheel is rotated by the motor. As a result of such rotational movement, air flow is drawn axially into the inlet(s) of the blower wheel and centrifugally discharged in a radially outward manner.
In other words, the blower wheel imparts velocity to the air travelling through the blower wheel as a result of two cooperating forces: (1) the centrifugal force caused by rotation of the air; and (2) the rotary force caused by contact between the air and the fan blades. As such, the fan blade design is an important factor in increasing the velocity and/or pressure of the air traveling through the blower.
In the fields of portable room air cleaners and humidifiers, it is especially important that the blower wheel be compact, highly reliable and efficient to move a large volume of air, while at the same time, displacing such air with a minimum amount of noise.
In an attempt to achieve these competing interests, a number of different fan blade designs have been utilized in centrifugal blower wheels. Such fan blade designs include, by way of example, radial blades that lie on radii of the hub, forward curved blades that are angularly displaced from the radial position in the direction of rotation of the blower wheel, and backward curved blades that are angularly displaced from the radial position against the direction of rotation of the blower wheel.
In addition, some fan blades are square cut, such that their inside edge projects upwardly and perpendicularly from the base plate of the blower wheel and is perpendicular to the distal end of the blade, or in some instances, may be slightly radiused where the inside edge joins the distal end of the blade. However, these square cut or modified square cut designs have a tendency to cause undesirable turbulence and noise during operation.
Still other blades have an inside edge that projects upwardly from the base plate at an angle to form a uniform taper along the entire length of the inside edge from the base plate to the distal end of the blade. However, this tapered blade design necessarily requires the blades to be wider proximate the base plate, thereby reducing the inside diameter formed by the blades proximate the base plate and limiting the relative output of the blower wheel.
In addition to the various fan blade designs, the design of the hub has also proven to be an important consideration. Bell-shaped or conical hubs have been employed with blower wheels to provide laminar, nonturbulent air flow patterns efficiently generated during the process of altering the air flow from its axial induction path to its radial discharge path. Since a large portion of the air flow leaving the hub and being discharged toward the fan blades contacts the blades at their proximal ends adjacent the hub, any nonlaminar, turbulent effect on the air flow pattern may cause undesirable noise and adversely affect the operation of the blower. Despite improvement in the air flow, however, there continues to be a need for the development of an optimal shape of the hub to improve the efficiency of the blower wheel and reduce overall noise.